strong nucleophiles

[joonkimdds]

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DAT destroyer often explains answers by saying
"since we got strong nucleophile we have this rxn...etc"

but it never explains what strong nucleophiles are.

Is there a list of strong nucloeophiles that I can memorize?
or is it better to memorize the definition?
I remember reading about its definition couple of times before but I was never able to understand it once I see the actual examples
so I prefer to just memorize all the list if there is one.

 

[Intrigue]

one thing I know is that strong bases are also strong nucleophiles.
water is a weak base so it is a weak nucleophile. hydroxide ion is a strong nucleophile.
Hope this helps!!

 

[PooyaH]

Good Nucleophiles would be: Br-, HO-, RO-, CN-, N3-
And these would be strong nuclephiles: HS-, RS-

 

[iwannabadentist]

Good Nucleophiles would be: Br-, HO-, RO-, CN-, N3-
And these would be strong nuclephiles: HS-, I-, RS-

hmm ru sure that I- is a strong nucleophile? Because I- is a very weak base considering that HI is the strongest naturally ocurring acid!

 

[PooyaH]

hmm ru sure that I- is a strong nucleophile? Because I- is a very weak base considering that HI is the strongest naturally ocurring acid!

Yes, you are correct, I shouldn't have included that!

 

[nze82]

Strong nucleophiles are generally those species with the following features:
1-They bear a negative charge-->This should be obvious, because anything bearing a negative charge is strongly attracted to a positively charge C atom. Therefore, it has a greater tendency for attacking it. Hence, it becomes a stronger nucleophile.
2-Large in size-->Larger species are more polarizable. Think about it; the larger the attom, the further away the electrons. Subsequently, the nucleus has a weaker "pull" on the electron, which means these electrons have more freedom to move toward a positively charged C atom and attack it.

Hope this helped.

 

[jlt0530]

hmm ru sure that I- is a strong nucleophile? Because I- is a very weak base considering that HI is the strongest naturally ocurring acid!

I used to mix these up too, but after missing several questions, im pretty sure that I- is a strong nucleophile. The way i understand nucleophilicity is

1. for example, when comparing nucleophilicity of OCH3- vs OH-
i look at their basicity. Since OCH3- is more basic than OH-, OCH3- is a better NUC than OH-.

2. But, when it comes to comparing nucleophilicity of the two atoms of the same column, larger the atom, better NUC. As we go down on the periodic table, atoms get larger, so they are the better NUC.
So, for such reason, SCH- is better NUC than OCH- and I- is better NUC than Br- which is a better NUC than Cl-.

I'm not sure this is the best way to look at it, but it has worked for me. If anyone has a better way to dintinguish nucleophilicity of atoms, I would like to know them too. 🙂

Hope this helped!